1. Field of the Invention
The invention relates generally to automatic clothes dryers, and, more particularly the invention relates to a method of determining a drying time for an automatic clothes dryer.
2. Description of the Related Art
Automatic clothes dryers are well known, and typically comprise a cabinet enclosing a horizontally rotating drum accessible through an access door at the front of the cabinet for holding clothing items to be dried. A heater positioned in an air inlet assembly upstream of the drum is utilized for heating the drying air prior to its entry into the drum. The drying air is delivered to the drum through a motor-driven blower assembly. A temperature sensor is utilized in an air outlet assembly downstream of the drum for monitoring the temperature of the exhausted air and determining when drying is complete.
During the drying cycle, the heater is sequentially energized and deenergized to increase and decrease the temperature of the air entering the drum. The heater is energized until the temperature of the air reaches a preselected limit temperature, at which time the heater is deenergized. The temperature of the air is allowed to decrease until a preselected reset temperature is reached, at which time the heater is reenergized. The cycle is repeated until the clothes reach a preselected dryness state, at which time the heater is deenergized and a cool down period occurs, during which the drum continues to rotate with unheated air flowing therethrough.
In a mechanical-timer-based dryer, the duration of the drying cycle is set by simply selecting a time duration, or by selecting a combination of clothes load characteristics (e.g. bulky items, woolens, normal, etc.) and a desired degree of dryness to be achieved at the end of the cycle. With either method, a mechanical timer is set and advances only during those time periods when the heater is deenergized, until the time expires.
A typical automatic clothes dryer also incorporates a moisture sensor in the drum, which consists of a pair of electrical contacts in close proximity to each other which are exposed to impacts by the clothes in the drum as the drum is rotated. When a wet article of clothing “bridges” across the sensor contacts, a circuit is closed, and this circuit closure is recorded in the dryer's control module. Circuit closures are accumulated over a preselected period of time and processed in the control module to arrive at a resulting number of “wet hits.” The wet hits are used as a measure of the size of the clothes load in the drum. The number of wet hits can be used to adjust the duration of the drying cycle. A common way to do this is to determine an “Add On” dry time that is determined by the remaining moisture content of the load and drying cycle parameters selected by the user. This methodology is described in U.S. Pat. No. 6,446,357 to Woerdehoff, et al., which is incorporated herein by reference.
If the number of wet hits is below a preselected value, this can indicate several conditions: the clothes load is small or the drum is empty, the moisture sensor is not operating properly, or the clothes load is relatively dry to begin with. In each case, it would be preferable to adjust the drying time during the drying cycle to accommodate such conditions. However, conventional dryers will continue to operate through a preselected cycle without modification based upon the predetermined drying time, which can result in overheating of the clothes, with accompanying excessive shrinkage or damage, excess energy usage, and increased wear on the dryer components.